The present invention relates, generally, to a resonator system and a method for resonator tuning.
Resonators are subject to certain manufacturing fluctuations in production. Furthermore, aging and temperature fluctuations occur during operation. This has the effect that the frequency position of a circuit resonator used in a circuit generally does not correspond exactly to the manufacturing specifications and also can vary over the course of time.
However, it is of crucial importance, particularly in the case of modern telecommunications devices, such as, for example, mobile telephones and other mobile terminals, that circuit resonators are used with a frequency position that is predetermined as exactly as possible. This is all the more true for direct conversion methods, whose use is spreading and which can only be achieved with filters that operate extremely precisely.
To date, resonators in the form of surface acoustic wave components have been used for filters in the abovementioned area of use. Such surface acoustic wave components are disclosed, for example, in DE 198 60 058 C1, EP 0 746 775B1, EP 0 655 701B1, EP 0 651 344B1, EP 0 619 906B1, U.S. Pat. No. 5,691,698, U.S. Pat. No. 5,841,214, U.S. Pat. No. 5,966,008, U.S. Pat. No. 5,910,779, U.S. Pat. No. 6,029,324, U.S. Pat. No. 6,084,503. They are distinguished, in particular, by a high long-term stability.
Unfortunately, these surface acoustic wave components cannot be integrated into semiconductor technology, for which reason hybrid solutions have to be pursued. In order to depart from these hybrid solutions, FBARs(Film Bulk Acoustic Resonators) are known, which can be produced at least partly in CMOS-compatible fashion. In this case, however, the required frequency accuracy cannot be mastered in terms of production engineering, so that mass production and, hence, low prices are not available.
U.S. Pat. No. 5,428,829 describes active filters which are integrated in semiconductor technology; in particular, in CMOS technology. An active filter circuit is excited to effect oscillation via specific settings of gain and phase angle and is used as an oscillator in a PLL. Quality factor and center frequency can be regulated by electrically tunable resistors and capacitors in the form of external circuitry in CMOS.
Taking this as a departure point, the present invention is directed toward a resonator system and a method for resonator tuning which can be used to compensate for production, temperature and aging fluctuations of the resonators. Furthermore, the resonator system and the method for resonator tuning are intended to be suitable, in particular, for microstructured and integrated components.